Current rotorcraft typically achieve controlled flight through the use of a swashplate as shown in FIG. 1. A pilot moves controls 110 which are coupled physically, hydraulically, or electrically to control linkages 120 that do not rotate with the rotor 130. The control linkages 120 can move a swashplate 160 up and down 162 in a collective move or tilt 164 the swashplate 160 in a cyclic 164 mode. The swashplate 160 transfers the motions of the non-rotating control linkages 120 to rotating pitch links 170. The pitch links 170 are coupled to blades 180 such that the blade is caused to rotate about its pitch axis 182. Collective control of blade pitch varies the thrust produced by the rotor, while cyclic control of blade pitch is used to control the direction of rotor force and moment. A pilot usually achieves vehicle directional control primarily through these collective and cyclic controls.
Cyclic input on a normal swashplate is usually constrained to a simple harmonic input with a frequency of one peak per rotor revolution. When the pilot commands cyclic control, the control linkages tilt the swashplate, causing one location of the swashplate to be higher than the rest of the swashplate. When a pitch link passes over this high point, the pitch of the blade is raised, which leads to increase in lift in the vicinity of the high portion of the swashplate.
Such swashplate systems are well-established in the rotorcraft industry. While swashplates offer a means of controlling a rotorcraft, they are large, heavy, complex, and prone to failure. The bearings necessary to transfer motion from non-rotating control linkages to rotating pitchlinks need lubrication and may fail. The mechanical or hydraulic systems associated with such a system are almost invariably complicated, and burden the rotorcraft with additional weight. Mechanical and hydraulic systems also have higher failure rates and maintenance requirements than all-electric systems.
It is further known in the industry that helicopter vibration can be reduced if the pitch of the rotor blades can be controlled at frequencies other than the simple cyclic control input with a frequency of one peak per rotor revolution. This is referred to as individual blade control.
One such system that achieves control of individual blade control is that of U.S. Pat. No. 6,666,649 ('649 patent) to Arnold shown in FIG. 2. Arnold combines a conventional swashplate with active pitch links 200 that are activated in the rotating frame. The pitch links must receive hydraulic fluid and electrical control signals through a slipring, which transfers fluid and electricity from the fixed frame to the rotating frame. Because the system of Arnold requires both a conventional swashplate and a slipring, it has complexity and weight exceeding that of a normal rotorcraft. The additional complexity and weight of the Arnold system make it impractical for use on rotorcraft.
The '649 patent and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. Unless a contrary intent is apparent from the context, all ranges recited herein are inclusive of their endpoints, and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary.
Another system that achieves individual blade control was developed by ZF Luftahrttechnik™ and described in the 2008 paper “Experimental Verification of an Electro-Mechanical-Actuator for a Swashplateless Primary and Individual Blade Control System”. The prior art ZF actuator concept is shown in FIG. 3. In this system, the swashplate is eliminated in favor of an electric slipring, which transfers electric power from the fixed frame to the rotating frame. As used herein, the term “swashplateless rotor” means a rotorcraft rotor not having a swashplate. Removal of the swashplate significantly reduces weight and complexity. The prior art ZF actuator 300 has a multiple phase redundant electric motor 310 that is coupled to a rotary gearbox 320 to drive the pitch of the rotor blades. The phase redundant electric motor is key to achieving fault tolerant vehicle control in flight. The prior art ZF actuator has a key disadvantage as compared to a conventional swashplate system or the Arnold system in that the ZF actuator is subject to some of the loads transferred from the rotor to the hub. Additionally, the use of rotary gearbox causes increased weight, relatively higher transmission losses, and is subject to backlash. This prior art system was designed for used on the prior art CH-53G helicopter which has an articulated (or hinged) rotor system.
Electric linear actuators, such as the planetary roller screw actuator described by Waide in US Patent Application 2006/0266146 are free of the problems of actuators coupled to rotary gearboxes. Shown in FIG. 4, the Waide actuator is designed to replace the fixed-frame control linkages coupled to the swashplate, and thus still requires a heavy swashplate. Furthermore, the Waide actuator does not have a multiple phase redundant electric motor beneficial to fault-tolerant flight control.
Other linear actuators use inverted rollers screws. See e.g., U.S. Pat. Nos. 5,491,372 and 5,557,154 to Erhart. Those actuators are not fault tolerant, do not include redundant motors, and have not been contemplated for individual blade control.
Therefore, what is still needed is a rotorcraft rotor blade control system that has reduced maintenance requirements, weight, complexity, and increased reliability. It should further be fault-tolerant, of low weight, and capable of reducing rotor vibration.